Thermionic valve system



Sept.- 6, 1932.

H ANDREWES 'THERMIONIC VALVE SYSTEM Filed April 18, 1931 l/l YEN TOR Patented Sept. 6, 1932 T D mm HUMFREY ANDREWES, or LonnoN, EN LAND; Assrcnon, BY MESNE ASSIGNMENTS, To

. BRITISH RADIOSTAT CORPORATION, LIMITED, .4; conroan'rron on CANADA PATENT: OFFICE 1 THERiIIoNIc vALvE SYSTEM Application filedii rir1s,'1931,; ser1arm 531,210, and. in Great Britain May 7, 1930.

7' This invention is for improvements in or relating to thermionic valve systems, such'as for example receivers and/or amphfiers for modulated or interrupted wave signals: In such systems it is necessary that the energy being dealt with should always be within thelimits, for example with regard to amplitude, to which the system. is designed,

since variations beyond this limit may produce distorted eflects due to saturation or overloading. F or instance it is usuallyv nee? essary to apply a bias or working potential to one or more of the electrodes ofa thermionic valve in order that it should operate in the required manner. In many cases the best value for the bias or working potential is determined to a large extent bythenature and amplitude of the energy which is applied to the system and shouldthe amplitude vary considerably, then it may be advantageous to vary the potential accordingly.

The present invention comprises a thermionic valve system wherein there is pro- 7 videdmeans automatically controlled by the amplitude of w the energy developed in the system for varying the operating conditions of the system in order that they shall always be appropriate to the amplitude of the energy tobe dealt with. Thus, by controlling the system, for example as regards the degree'fof amplification or its'working adjustment in an automatic manner according'to the energy to be dealt with, the system will always operate within the limits for which it.is designed a and in the best manner according to'the en- 7 ergy applied to it.

In one application of the invention, it is applied to highly selective receivers for modulated or interrupted carrier wave signals such, for example, as those described in .the U, S. Letters Patent to J ames Robinson, Nos.

1,821,032 and 1,821,033 granted September 1 that the modulation (e. g. in carrier wave telephony) is a very low percentage of the carrier wave that is applied to the valve, and necessitates an unusually large negative bias forthe valve.

The prior patents-above referred to fur-- ther provide means whereby the selectivity of the several circuits illustrated therein may be materlally reduced in order to facilitate tuning of these circuits, and when theselectivity of the circuits is thus reduced, the ab.- normally large negative bias for the valve interferes with the transmission of signals by selectivity is accompanied by a corresponding increase in the percentage modulation of the signal transmitted through the tuning circuit, and the signal amplitude is correspondingly increased. Thus it is essential in a highly selective receiver of this type to provide for automatic variation of the grid bias on the valve in accordance with the variation in selectivity of the receiver.

It is thus an object of the invention to provide a receiving system employing a highly selective device, the electrical output of which is applied to a thermionic valve and means automatically controlled by the energy developed at the selective device for applyinga bias potential to the said Valve, whereby this biasing potential shall always be appropriate to the energy to be dealt with by the valve;

Inone form of the invention, a portion of the energy in the system (c. g. at a point following a highly selective device) is applied to an auxiliary circuit including a rectifier for providing a controlling potential varying according to the amplitude of the signals.

, One specific embodiment of the invention is shown diagrammatically and by way of example in the accompanying drawing as Referring to thedrawing, the signals with reason of the fact that the reduction of the i or without previous selection and amplification are applied through an input coil 10 to a tuned circuit 11 comprising an inductance 12 and variable condensers 13. A pieZo-electric device 14 is connected in series between one side of the tuned circuit and the input electrode of a valve 15. A variable condenser 16 is connected between the other side of the tuned circuit 11 and the input electrode of the valve 15, and the cathode of this valve is connected direct to the junction between the condensers 13 of the tuned circuit 11. This balanced arrangement of the piezo crystal 14 and the condenser 16 serves to minimize the effects of any interference passing the piezo-electric device as described in the patent application of James Robinson, Serial N 0. 460,054.

A leak impedance for the valve 15 is constituted by a tuned circuit 17 with a bias battery 18 in series therewith, a bypass condenser 19 being connected in parallel with the battery.

It will be observed that the'circuit'thus far described constitutes a highly selective resonator for applied energy, and while it is a feature of the present invention that the resonator is characterized by unusually high selectivity, it is apparent from an inspection of the aforementioned prior United States patents that this resonator may assume various forms, of which the arrangement shown in the present application and constituting the preferred form is merely illustrative.

The output circuit of the valve 15 includes a coil 20 which is coupled to another coil 21 tuned by means of a condenser 22. One side of the tuned circuit 21, 22 is connected to the input electrode of a thermonic valve 23 which is arranged to operate as a detector and the other side of this tuned circuit is connected through a condenser 24 to the cathodes of the valves. The output circuit of the valve 23 includes the primary winding of a transformer 25, the secondary winding of which provides the signal'output which may for eX- ample be fed to an amplifier for the signals.

It will be appreciated that if the selectivity of the system be reduced for example by turning the condenser 16 out of adjustment in order to facilitate picking up the required signals, a large fixed negative bias may completely stop signals passing the valve 23, and in order that this valve may deal with the signals in these circumstances, a much reduced negative bias is required. This difiiculty is overcome by the provision of means for automatically varying the negative bias on the valve as the selectivity of the receiver and the consequent signal intensity due to persistence is varied as described hereinafter.

In the system shown in the drawing, a portion of the signal energy in the coil 20 is fed to another coil 26 connected in series with a accordin thermionic valve rectifier 27 across the condenser 24.

The signal energy introduced into the coil 26 and rectified by the valve 27 is thus applied through the coil 21 as a biasing potential for the control electrode of the valve 23 and the value of this potential will vary to the amplitude of the signal energy. Thus when the signal energy is large as in the case when the system is operating in a highly selective condition, the negative biasing potential will be correspondingly large and when the signal energy is comparatively small, the negative bias will be reduced correspondingly. An inductive choke '28 and condensers 29' are provided for smoothing the negative potential effect.

Thebia'sing potential obtained from the signals may be ap lied to any of the valves in the system in a dition to or instead of the detector valve in order to provide automatically controlled bias for such valves. Moreover for providing the control bias the energy may be obtained from any part of the system following the highly selective device and not necessarily from the valve immediately following this device, as in, the specific example described above. f

Furthermore, it will be understood that selective devices other than a piezo-electric crystal may be employed, such, for example, as a tuning fork, a retroactive thermionic valve circuit or a plurality of tuned circuits coupled in cascade.

In a modification in which the gain of a receiver or amplifier is to be controlled according to the amplitude of the signals, the potentials obtained from the signals instead of being applied as a biasing potential as in the specific case above described, may be used to control the degree of amplification of a valve or valves in the system. If desired, the signal effects which are to provide the bias potential, may be separately amplified before rectification, and furthermore additional biasing batteries may be employed for providing in conjunction with the potentials obtained from the signals, the required range of potential variation for controlling the system. v 1

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In wave signalling apparatus, the combination with a highly selective resonator for 1 applied modulated wave energy, a detector valve to which the energy output of said resonator is supplied, the degree of selectivity of said resonator being such that the percentage modulation of the energy supplied to the valve is materially reduced, whereby an abnormally high bias potential is required for the valve, means operable to reduce the degree of selectivity of said resonator whereby the percentage of modulation lg ing the bias potential supplied to the valve as the degree of selectivity of said resonator is reduced.

2. In wave signalling apparatus, the com-' bination with a highly selective resonator for applied modulated wave energy, a detector valve to which the energy output of said resonator is supplied, the degree of selectivity of said resonator being such that the percentage modulation of the energy supplied to the valve is materially reduced, whereby an abnormally high bias potential is required for the valve, means operable to reduce the degree of selectivity of said resonator whereby the percentage modulation of the applied energy is increased by reduction of the absolute signal amplitude, and means comprising a source of bias potential energized by the energy output of said resonator for decreasing the bias potential supplied to the valve as the degree of selectivity of said resonator is reduced.

3. Thermionic valve apparatus for modulated Wave signal energy comprising the combination of a highly selective resonator for the energy, the selectivity of said resonator being such that the percentage modulation of the energy output thereof is materially reduced, means for adjusting the degree of selectivity of said resonator whereby the percentage modulation of the signal energy and thereby the signal amplitude is changed, a thermionic valve detector to which the energy output from said resonator is applied, and means controlled by the energy developed in the selective device for applying to the said valve an operating bias potential automatically varying according to changes in amplitude of the signals delivered by the said resonant device.

4;. Radio receiving apparatus comprising the combination of a piezo-electric device for applied signal energ means whereby the degree of selectivity of this piezo-electric device is varied whereby the amplitude of the output signal energy of the device is changed, a thermionic valve detector to which the signal energy from said piezo-electrio device is supplied, and means controlled by the energy output of the piezo-electric device for applying an operating bias potential to the said valve whereby the operating characteristic of the valve is always appropriate to the signal amplitudes.

5. In wave signalling apparatus, the combination with a highly selective resonator for applied modulated Wave energy, a valve to which the energy output of said resonator is supplied, the degree of selectivity of said resonator being such that the percentage 1 valve is materially reduced, whereby an abnormally high bias potential is required for the valve, means operable to reduce the degree of selectivity of said resonator whereby the percentage modulation of the energy supplied to the valve is increased by reduction of the absolute signal amplitude,and means controlled by operation of said last named means for decreasing the bias potential supplied to the valve as the degree of selectivity of said resonator is reduced.

In testimony whereof I have signed my name to this specification.

HUMFREY ANDREWES. 

